1. Field of the Invention
The invention relates to a drill bit for drilling subterranean formations, and particularly to a drill bit construction that will provide stabilization of the drill bit against radial vibration.
2. Summary of the Prior Art
When drilling well bores in subsurface formations, it often happens that the drill passes readily through a comparatively soft formation and then strikes a significantly harder formation. Rarely do all of the cutting elements mounted on conventional drilling bit strike the harder formation at the same time, hence a substantial impact force is incurred by the one or two cutting elements that initially strike the harder formation, resulting in a sidewise deflecting force being applied to the entire drilling bit. The end result is the creation of radial vibration of the drilling bit relative to the axis of rotation, resulting in either an enlarged well bore or a well bore having axially spaced grooves in the bore wall. Substantial wear or even destruction of those cutting elements initially striking the harder formation is an additional problem.
The problem of vibration of a drilling bit is particularly acute when the well bore is drilled at a substantial angle to the vertical, such as in the recently popular horizontal drilling practice. Here, the drill bit and the adjacent portions of the drilling string are constantly subject to the downward force of gravity and a sporadic weight on bit, producing unbalanced loading of the cutting structure, which can result in radial vibration. Prior investigators of the effects of vibration on a drilling bit have developed the phraseology of "bit whirl" to describe the phenomena. See SPE Paper #19572 by T. M. WARREN et al entitled: "Development of a Whirl-Resistant Bit". The only viable solution proposed by this investigation was the utilization of a low friction gauge pad on the drill bit, but the writers admit that this technology is still being refined. It follows that a practical preventive solution to the problem of vibration of a drilling bit would be highly desirable, particularly for use in directional drilling of wells.